Phys.org  September 9, 2022 Researchers at Purdue University have proposed the generation of attosecond entangled biphotons in the extreme-ultraviolet regime by two-photon decay of a metastable atomic state as a source like spontaneous parametric down-conversion photons. The 1s2s1S0 metastable state in helium decays to the ground state by the emission of two energy-time entangled photons with a photon bandwidth equal to the total energy spacing of 20.62 eV. This results in a pair correlation time in the attosecond regime making these entangled photons a highly suitable source for attosecond pump-probe experiments. They calculated and used the biphoton generation rate from […]